Feb 21, 2007

Stunning color pictures from Mars offer new evidence that plentiful groundwater once percolated through Martian bedrock.The new images, taken by NASA's Mars Reconnaissance Orbiter, reveal a terrain of banded rocks similar to that found in the southwestern U.S., said Chris Okubo, a postdoctoral researcher at the University of Arizona's Lunar and Planetary Laboratory.

The new pictures show that Martian rocks in this sandy landscape are riddled with small cracks.These cracks bear telltale signs that fluid—probably water—seeped through them hundreds of millions of years ago.Prominent riblike structures along the cracks, for instance, suggest that running water dissolved minerals in the Martian soil, forming a kind of cement.The water also dissolved dark minerals out of the rocks, leaving light-colored "halos" around the cracks.These findings are exciting, because they suggest that similar water-filled fractures might still exist beneath the Martian surface, scientists said."What we see at the surface today are glimpses of what used to be underground," Okubo said.Okubo presented the new images at a press conference today in San Francisco, California.

Since telescopes were first aimed at Mars, astronomers have noticed the planet's distinctive light and dark patches. Some of the patches change position as winds blow dust and sand across the surface. Brighter areas may indicate places that in the recent past have been coated with fine-grained material. Some dark areas are permanent features, such as the huge ring of dunes around the north polar cap. Other dark areas have been swept partly clear to reveal older rock beneath.

To create this global portrait, technicians combined some one thousand images taken by Viking Orbiters in the 1970s. The brightest area in the image is the north polar cap. Seen here in summer at its minimum size, the permanent cap covers an area about 1.5 times the size of Texas. It is the only known place where frozen water is stable on the Martian surface.

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